This is quickie. The knee and the slides etc that it supports on a knee mill is very heavy. The effort required for manual or motor powered movement is considerable. A while back I converted my Bridgeport to motorised knee movement and while I was at it I decided to give the motor an easier time by relieving some of the weight. I had a few of those tailgate pneumatic springs fitted to many cars. I tend to save things like that when I'm done with a car. I put two on each side of the mill centred around the lift screw.
Four of these spring units relieve much of the weight of the knee. This has several benefits in addition to the obvious one of making it easier to raise the knee, it reduces wear on the lift screw and nut, but it also relieves load on the slides. The ratio between benefit and effort is quite high.